Flexible tank and method of making such a tank

ABSTRACT

Provided is a flexible tank and method of making such a tank.

CROSS REFERENCE

This application is a continuation of U.S. patent application Ser. No. 10/239,474, as filed on Sep. 20, 2002 entitled “A FLEXIBLE TANK AND METHOD OF MAKING SUCH A TANK”, which claims benefit of International Patent Cooperation Treaty Application PCT/IB01/00486, filed on Mar. 22, 2001, which claims priority benefit from Great Britain Patent Application Number 0006973.2, filed Mar. 22, 2000.

BACKGROUND OF INVENTION

The present invention relates to a flexible tank for bulk liquids and a method of making such a tank. In particular, the invention relates to a disposable flexible tank.

Flexible tanks, or flexitanks, are bulk containers that are used for storing and transporting fluids. These tanks can be constructed from a variety of robber or thermoplastic materials and typically have capacities of up to 24,000 litres. In use flexitanks are used inside dry goods containers, thereby converting such containers into bulk liquid containers capable of carrying up to 21.5 tonnes of non-hazardous liquid product.

One known flexitank is made from a woven nylon or polyester fabric coated on both sides with synthetic rubber or thermoplastic material. The coating is done using a process called calandering. This is a re-usable tank, with a life span of, typically, five years. A disadvantage of this tank is that it requires re-cleaning after every use, which can cause contamination and environmental concerns. In addition, a large infra-structure is required to operate, handle, clean, service and return the tank. This means that there is a high capital cost associated with the running of the business. Furthermore, in practice, tanks of this type are subject to quality problems.

Due to the problems associated with re-usable tanks, there has been a trend in the market towards disposable or one-use flexitanks, typically made of thermoplastic (PVC). A disadvantage of these tanks is, however, that they are subject to quality problems, with leakages being relatively common.

An object of the present invention is to provide an improved flexitank, in particular an improved disposable flexitank.

According to the present invention, there is provided a flexible tank that comprises a one piece body portion that is formed using blowing techniques.

An advantage of this is that it minimises the number of seams required to form the tank. This means in practice that the tank is less susceptible to leakages.

Preferably, the one piece body portion is a seamless tube. The ends of the tube may be closed by, for example, welding.

Preferably, two one piece body portions are provided, one forming an inner liner and the other forming an outer liner.

The one piece body portion may be made of polyethylene, preferably a blend of resin and bonding agent. The ratio of the resin to bonding agent may be 75% to 25%. Preferably, the resin is Elite (Metallasin) 5100 resin (C6 Linear low density polyethylene (LLDPE)) made by Dow Chemicals. The bonding agent may be a co-polymer, preferably ethylene butyl acrylate (EBA).

The or each body portion may comprise two or more layers, for example three or four. Preferably, the body portion is co-extruded. Preferably, the body portion comprises two layers. The two layers may be of different polyethylene, one being, for example, a high density polyethylene, the other being a low density polyethylene.

According to another aspect of the present invention, there is provided a method of forming a flexible tank using blown film techniques to form a one-piece seamless body portion.

Preferably, the one-piece seamless body portion is a tube. The ends of the tube are preferably closed by, for example, welding.

Preferably, the step of blowing the tube comprises co-extruding at least two layers of material to form the body portion.

Preferably, two one piece body portions are provided, one being an inner liner and the other being an outer liner.

The one piece body portion may be made of material that comprises a blend of resin and bonding agent. Preferably, the ratio of the resin to bonding agent is 75% to 25%. Preferably, the resin is Elite (Metallasin) 5100 resin (C6 LLDPE) made by Dow Chemicals. The bonding agent may be a co-polymer, preferably EBA.

Various flexible tanks and methods for making such tanks in which the present invention is embodied will now be described by way of example only and with reference to the following drawings, of which:

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a side view of a seamless tube of material for making a flexitank;

FIG. 2 is a plan view of the tube of FIG. 1;

FIG. 3 is a side view of an outer tubular liner into which is inserted the inner liner of FIG. 2;

FIG. 4 is a section on the line III-III of FIG. 3;

FIG. 5 is a section through a seam for sealing the inner and outer liners of FIGS. 2 and 3;

FIG. 6 is a plan view of a flexitank that is sealed in the manner shown in FIG. 5;

FIG. 7 is an alternative seam arrangement for sealing inner and outer flexitank liners;

FIG. 8 is a plan view of a flexitank that is sealed in the manner shown in FIG. 7;

FIG. 9 is a side view of a flexitank that includes an in-transit hose protector;

FIG. 10 is a plan view of yet another flexitank;

DETAILED DESCRIPTION

FIG. 1 shows a seamless, open-ended, one piece tube of material 10. This seamless tube 10 is formed using a blown film technique, which involves liquifying constituent materials, extruding them through a die and blowing them into a large bubble. In one example, the material liquified is a 75%:25% mix of Elite (Metallasin) 5100 resin (C6 LLDPE) made by Dow Chemicals and co-polymer EBA. In order to make a 23,000 litre capacity tank, the bubble formed is about 7 m by 4 m, typically 7.3 m by 4.04 m. The thickness of the material of the bubble is typically 225 micrometers, but may be as much as 250 micrometers. The bubble is cut to form a seamless tube.

The seamless tube 10 is used as an inner liner 10 for a flexitank. Two holes are formed through the liner 10, as shown in FIG. 2. Surrounding one hole is a male flange 12; surrounding the other hole is a female flange 14. To seal the ends of the inner liner 10, seams 16 are formed, typically, 50 ram from the edges of the tube 10. These seams 16 are welded.

Once the ends of the inner liner 10 are sealed, it is placed inside a similar, but larger outer liner 18, as shown in FIG. 3. A collar 20 is welded to the male flange 12 on the inner liner 10 and the outer liner 18, as shown in FIG. 4. This collar 20 extends through the outer liner 18 and is adapted to receive the end of a hose for filling and emptying the tank. Connected to the female flange 14 is a pressure relief valve (not shown) for ensuring that the internal pressure of the tank does not exceed a pre-set level.

Once the inner and outer liners 10 and 18 respectively are correctly positioned, the ends of the outer liner 18 are sealed together, as shown in FIG. 5. A tank formed in this way is illustrated in FIG. 6, which shows a 7470 mm by 3950 mm sealed inner liner 10 inside a 7670 mm by 4850 mm sealed outer liner 18.

In an alternative arrangement, the ends of the inner liner 10 are not sealed separately prior to insertion into the outer liner 18, but instead the ends of the inner and outer liners 10 and 18 are sealed together at one position, as shown in FIG. 7. A tank sealed in this way is shown in FIG. 8. In this case, the width of the outer liner is identical to or very slightly larger than that of the inner liner, although it is longer.

Each of the inner and outer liners described above is fully sealed. This means that both primary and secondary containment are provided. This is advantageous because in the unlikely event of the inner liner being damaged, the outer liner can still fully, contain any leakage.

In use a hose 22 is attached to the collar 20, as shown in FIG. 9. To prevent the hose from falling around during transportation, in-transit hose protectors 24 are attached to the outer liner 18. These protectors have straps 26 that can extend around the hose. Each strap is welded to the outer liner at several points along its length. Buckles 28 are provided at one end, so that the straps 26 can be wound round the hose 22 to hold it against the tank and then secured to the buckles.

Early tests show that the following technical specifications can be achieved using the inner liner described above:

-   -   Thickness: 221 micrometers     -   MD Tensile strength: 29.5 Mpa     -   TD Tensile strength: 36.4 Mpa     -   MD Elmendorf Tear:22.5 micrometers     -   TD Elmendorf Tear: >30 g/micrometer     -   Low temperature flexibility: −25 C.     -   High temperature flexibility: 70 C.     -   Dart Impact: 1100 g     -   Melt Point Index:0.8

Whilst the flexitanks of FIG. 1 to 9 have an inner liner 10 and an outer liner 18, the flexitank can be formed from a single liner having two layers, each of which performs different functions. This liner is made from a blown film, which is double co-extruded, i.e. formed by extruding two liquified components at the same time. In this, the inner liner has two layers, one of which is a 225 gm layer of the 75% to 25% mix of Elite (Metallasin) 5100 resin (C6 LLDPE) and EBA, the other of which is a 225 gm polyethylene (PE) outer layer. This outer layer is provided to improve the strength of the tank and replaces the outer liner 18 of the previously described embodiments. Of course, the single liner flexitank could be made from more than two layers of PE.

It will be appreciated that the dimensions of the flexitank can be varied. In the example of FIG. 2, the inner liner is 7470 mm long and 3950 mm wide, as measured when flat.

The inner liners of all of the flexitanks described above are formed using a blown film tube. This means that the tube has no panels, no welds and no seams. This is advantageous because it means that the flexitank is less prone to leaking and so the quality is improved. In addition, the use of blowing techniques enables a co-extrusion process to be employed. This means that two or more layers of material, e.g. polyethylene, can be bonded together to perform different functions.

A further advantage of the flexitanks in which the present invention is embodied is that they are less susceptible to leaking than known tanks and so provide improved performance. Tanks can be manufactured to exceed industry standards at a lower cost than existing technology. All of the liners described above can be made relatively cheaply to conform and comply with standards set by the FDA, the BGA and the Japanese Canning Authority. Furthermore, they show good puncture resistance, impact strength and good tear strength.

A skilled person will appreciate that variations of the disclosed arrangements are possible without departing from the invention. Accordingly, the above description of specific embodiments is made by way of example and not for the purposes of limitation. It will be clear to the skilled person that minor modifications can be made without significant changes to the operation described above. 

1. A flexible tank that comprises a one piece body portion that is form using a blown film technique.
 2. A flexible tank as claimed in claim 1, wherein the one piece portion is a seamless tube.
 3. A flexible tank as claimed in claim 1, wherein the ends of the tube are closed, for example, by welding.
 4. A flexible tank as claimed in claim 1, wherein two one piece body portions are provided, one forming an inner liner and the other forming an outer liner.
 5. A flexible tank as claimed in claim 1, wherein the one piece body portion is made of polyethylene.
 6. A flexible tank as claimed in claim 5, wherein the one piece body portion is made of a polyethylene based resin and a bonding agent.
 7. A flexible tank as claimed in claim 6, wherein the ratio of resin to bonding agent is 75% to 25%.
 8. A flexible tank as claimed in claim 6, wherein the resin is Elite (Metallasin) 5100 resin (C6 Linear low density polyethylene (LLDPE)) made by Dow Chemicals.
 9. A flexible tank as claimed in claim 6, wherein the bonding agent is a co-polymer, preferably ethylene butyl acryiate (EBA).
 10. A flexible tank as claimed in claim 1, wherein the or each one piece body portion comprises two or more materials, preferably in layers, for example three or four.
 11. A flexible tank as claimed in claim 10, wherein a layer of the body portion comprises a flexible material.
 12. A flexible tank as claimed in claim 11, wherein the flexible material is polyethylene.
 13. A flexible tank as claimed in claim 10, wherein a layer of the body portion comprises a material that is adapted to reduce flex cracking.
 14. A flexible tank as claimed in claim 10, wherein the materials of the body portion are co-extruded during the blown film process.
 15. A flexible tank as claimed in claim 10, wherein the layers are made of different polyethylene, one being, for example, a linear low density polyethylene, the other being a low density polyethylene.
 16. A flexible tank as claimed in claim 1 comprising an outer liner.
 17. A flexible tank as claimed in claim 1, wherein the material of the body portion has a thickness in the range of 100 to 250 μm, preferable 120-130 μm, preferably substantially 125 μm.
 18. A method of forming a flexible tank using blown film techniques to form a one-piece seamless body portion.
 19. A method as claimed in claim 18, wherein the one-piece seamless body portion is a tube.
 20. A method as claim in claim 19, comprising sealing the ends of the tube, for example, by welding.
 21. A method as claimed in claim 18, wherein the step of blowing the tube comprises co-extruding at least two layers of material to form the body portion.
 22. A method as claimed in claim 18, comprising forming a plurality of one piece body portions and fitting the body portions inside each other.
 23. A method as claimed in claim 18, wherein the one piece body portion is made of material that comprises a blend of resin and bonding agent.
 24. A method as claimed in claim 23, wherein the ratio of the resin to bonding agent is 75% to 25%.
 25. A method as claimed in claim 23, wherein the resin is Elite (Metallasin) 5100 resin (C6 LLDPE) made by Dow Chemicals.
 26. A method as claimed in claim 18, wherein the or each one piece body portion comprises two or more materials, preferably in layers, for example three or four.
 27. A method as claimed in claim 26, comprising forming a layer of the body portion using a flexible material.
 28. A method as claimed in claim 27, wherein the flexible material is polyethylene.
 29. A method as claimed in claim 26, comprising forming a layer of the body portion using a material that is adapted to reduce flex cracking.
 30. A method as claimed in claim 26, comprising co-extruding the plurality of materials of the body portion during the blown film process.
 31. A method as claimed in claim 18, comprising forming an outer liner and locating the body portion in the outer liner.
 32. A method as claimed in claim 18, comprising forming the body portion so that it has a thickness in the range of 100 to 250 μm, preferably 120-130 μm, preferably substantially 125 μm. 